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Can someone enlighten me on the 05-07 CR pinging issue?

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Ok guys, so I discovered something last week related to the pinging I've been having on my '06 CR250.  When I bought the bike last year I did a top end before putting really any hours on it, and it had a ping, but not under acceleration.  It only did it after the rpm's dropped, right before settling back to idle.  Searching on here revealed that pinging is common on this model because of the crappy squish band in the head.  So my simple fix was to run 100LL gas from the airport, but it still sort of did it just not nearly as much.  

 

So last week I went on a ride at about 5,000' elevation in cool weather, which is the lowest and coldest I've ridden this bike in(I live at 7K and rode it up to 13K last year). I didn't have AV so I ran pump 91 and to my surprise, it didn't ping at all.  Weird.  So a few days ago I rode it here at 7,200(still with 91 pump) and it pinged as usual, but after turning the air screw in to about 1/4 turn I got it to go away.  Throttle response was a little sluggish, but I can live with it.  I'll probably go down a pilot now.  

So im stoked that I was able to solve this problem with just some tuning, but I'm still confused as to what causes this?  I always thought the ping was from too high compression and/or low octane fuel, which in this case was the opposite.  So this seems backwards to me.

But I also got to thinking about WHEN the ping occurs... it has never done it under any load at all, only when the engine revs drop just before returning to idle.  So was having the air screw too rich causing extra fuel to burn for another cycle with the throttle closed?  If a simple pilot jet change fixes this, maybe I'm overthinking things.  Just wondering if anyone else had thought of or experienced this. 

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The timing is currently stock, although I tried going advance and retard, neither made any noticeable difference.  Also no difference with the TPS disconnected or not, since I believe that affects ignition maps slightly.  

 

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No, but I'm aware that this is basically the real way to fix the ping.  I have plans to send the head to RB Designs, but wanted to get my other bike running first so I'm not without a ride.  

After adjusting the carb, the problem seems to have subsided, I was really just looking for technical explanation as to why this happens.  Just out of curious mainly.

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I've read about the pinging on the 05-07's since Honda bumped up the comp ratio on them vs. the 02-04 models.  Owned (2) 06's & (3) 07's with out any issues with pinging.  As you already found out jetting & running good fuel is the key.  RB Designs is a reputable machinists & would consider sending him any of my CR cyl heads to correct the squish band.   

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Was it a lot warmer when you rode at 7,200 feet compared to when you rode at 5,000 feet? If it was a hot day and your engine temperatures were up that may partially explain your phenomenon. I had a pinging issue at high temperatures with my '02 when I had a bad batch of gasoline which went away when I richened the mixture by turning in the air screw like you mentioned (causing the bike to run cooler, but too rich), and then I added a small bottle of stp octane booster and that completely eliminated the pinging until I was able to get fresh fuel. I recommend getting one of these radiator caps to monitor engine temperature and you can use it to draw correlations between engine temp and performance: https://www.rockymountainatvmc.com/p/917/61141/Tusk-High-Pressure-Radiator-Cap-with-Temperature-Gauge

 

 

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I had pinging issues on my 02 after a fresh top end. blew piston after 5 hours and checked my squish, shaved off about .005" and had it about .050" and started running AV 100ll 40:1 klotz and had no issues for 50-60hours when a crack along back cylinder wall leaned out and caused her to blow last year.

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I had that issue with my 2006 when I used Shell gas. Someone told me to try Esso which is Exxon in the US and that minimized the problem.  I'm no expert in the area of fuel blends but the Exxon fuel is different than what I was running. If you do send your head to RB Designs make it very clear in writing what you want. I know this from experience. 

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On 5/2/2017 at 2:12 PM, md30 said:

Was it a lot warmer when you rode at 7,200 feet compared to when you rode at 5,000 feet? If it was a hot day and your engine temperatures were up that may partially explain your phenomenon. I had a pinging issue at high temperatures with my '02 when I had a bad batch of gasoline which went away when I richened the mixture by turning in the air screw like you mentioned (causing the bike to run cooler, but too rich), and then I added a small bottle of stp octane booster and that completely eliminated the pinging until I was able to get fresh fuel. I recommend getting one of these radiator caps to monitor engine temperature and you can use it to draw correlations between engine temp and performance: https://www.rockymountainatvmc.com/p/917/61141/Tusk-High-Pressure-Radiator-Cap-with-Temperature-Gauge

 

 

Temps weren't too different.  Between 55-75 usually, it doesn't get too hot here.  In fact I don't think I've ridden this bike in any hotter than 85 degrees yet.  I actually went out yesterday in about 70 degree weather and it ran like crap, so I had to turn the air screw out little.  It pinged more, but I couldn't run it as before because it was bogging and spooging like mad. I don't know the real temps of the engine, bit I always feel like my bike runs cold.  I lug it mostly and it's jetted about a size rich on the main and pilot.  

 

Could be gas quality too.  New Mexico gas is probably not the most consistent so I think I'm gonna just keep running AV.  91 is close to $3.00/gallon, so AV being $4.90 isn't a bad deal if it saves my motor.  

 

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1 hour ago, Dklassen said:

I had that issue with my 2006 when I used Shell gas. Someone told me to try Esso which is Exxon in the US and that minimized the problem.  I'm no expert in the area of fuel blends but the Exxon fuel is different than what I was running. If you do send your head to RB Designs make it very clear in writing what you want. I know this from experience. 

I've been planning to send it out, but then again I said that last year, too!  I'm on the fence about about getting the cylinder shaved down 0.030" like a lot of people seem to do, because this bike is set up for enduro, and I'm only 145 lbs.  it has more than enough power for me, I just want a little more on the bottom end.  

Turning out the air screw/leaning the pilot gave me the bottom end response I wanted, but the pinging was much worse.  

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11 hours ago, Dklassen said:

If you do send your head to RB Designs make it very clear in writing what you want. I know this from experience. 

Can you elaborate ?  I haven't read or seen any negative feedback about his work on any forums. 

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